@serhiy-storchaka: I addressed your review. Please review the updated PR.

Oh, I don't think deepcopy of frozendict is correct. It does not work for recursive frozendict.

I will try to update my PR later to address other comments.

What about frozendict views and iterators? Are they copyable/pickleable?

keys, values and items views cannot be copied nor serialized by pickle.

Ah, it seems like it's possible to serialize a frozendict iterator.

Are there tests for deepcopying?

test_copy.test_deepcopy_frozendict() tests frozendict deepcopy.

I am surprised that there is no separate test_frozendict.py.

Ah. It was simple to add frozendict tests to existing test_dict. Maybe we can create test_frozendict later once we will add more tests.

Oh, I don't think deepcopy of frozendict is correct. It does not work for recursive frozendict.

You're right, the current copy.deepcopy() implementation doesn't work for recursive frozendict.

I completed the PR to add requested tests.

You're right, the current copy.deepcopy() implementation doesn't work for recursive frozendict.

I created #145027 to fix copy.deepcopy() for recursive frozendict.

If things are pickleable, they should also be deepcopyable. It is worth to have explicit deepcopy tests, because they can preserve additional invariants. For example, it should be possible to deepcopy a frozendict containing lambdas or modules.

I propose merging this PR first (once it will be approved), and then adding such tests to #145027 PR.

Did you forget to push changes for comments which you marked resolved?

Ooops, you're correct. I forgot to push my changes, but I also removed my local branch... I had to rewrite my changes. I just pushed them. I should be ok now.

Merged. Thanks for your great review @serhiy-storchaka, it was very useful!

This broke Oddballs (i.e. text_xpickle): https://buildbot.python.org/#/builders/1868/builds/5

This broke Oddballs (i.e. text_xpickle): https://buildbot.python.org/#/builders/1868/builds/5

Oh, I'm not used to test_xpickle yet, I forgot about it. I wrote #145069 to fix test_xpickle.